Unraveling the Changing Landscape of the Colorado and San Juan Rivers

Sometimes  . . .

Returning Rapids researchers relax while traveling across the Lake Powell reservoir. Photo credit: Cari Johnson

. . . geologic inquiry presents itself so forcefully and on its own timetable that researchers have little choice but to "go with the flow," as it were. That has certainly been the case of late in the American Southwest as mega-drought conditions have plunged the nation's largest reservoirs to new lows and terrain, underwater for decades, is quickly being daylighted.

 University of Utah geologists Cari Johnson and Brenda Bowen are at the forefront of a remarkable collaborative effort to understand the dynamic transformation of the river corridors entering the Lake Powell Reservoir, in particular the Colorado and San Juan Rivers. Just capturing a moment of unprecedented geological change in real time has proven challenging.   

Deep Time, Modern Moment

Brenda Bowen studies geologic features. Credit: Elliot Ross

Johnson, a deep time stratigrapher, brings a unique perspective to this contemporary geological puzzle. Traditionally, her work has involved studying sedimentary layers millions to billions of years old, deciphering ancient landscapes from rock formations.  But now she finds herself in an extraordinary "time machine"  — the Colorado River, its tributaries and their surrounding landscapes — where she can observe sedimentation processes in near real-time.

 "The Glen Canyon Dam, completed in 1966, created a closed lake basin that's essentially a living laboratory," Johnson explains. "We have an incredibly detailed instrumented record of lake-level history, river discharge, and sediment load. These records establish the known boundary conditions that acted to form the textures, and features we see in decades-old reservoir sediment along the Colorado and San Juan River corridors.” It's like a long term, regional-scale experiment that began with construction of the Dam, the results of which are exposed for us to study now, due to falling reservoir levels. Bowen complements Johnson's approach by focusing on geomorphic evolution in response to human infrastructure. Together, they're documenting how sediment moves, changes, and impacts the landscape.

 "We're not just collecting data," Bowen emphasizes. "We're contributing to an interdisciplinary community trying to understand active landscape changes and potentially inform management decisions."

Motoring around a bend. Credit: Elliot Ross

Returning Rapids

Central to their work is the Returning Rapids project, a collaborative effort that brings together researchers, government agencies, nonprofit organizations and tribal representatives. This initiative has been crucial in providing access to remote and challenging terrains, facilitating unprecedented interdisciplinary research. In a recent Rolling Stone article the breathless pace and dynamism of the rapidly changing Cataract Canyon features Returning Rapids, river-rafting enthusiasts who consider Cataract Canyon a second home and whose name counters the conventional view of many that “the emerging landscape as an area that will one day be under water again, even though the data suggests the opposite.”

 "Returning Rapids doesn't just give us physical access," Johnson notes. "They bring together fish biologists, riparian ecologists, geologists, policymakers, land management agencies and others to create a comprehensive understanding of the landscape."

Mud Volcanoes

Credit: Elliot Ross

Johnson and Bowen’s research has yielded fascinating discoveries. One particularly intriguing finding is the presence of "sediment volcanoes" — small mud formations that emerge as reservoir levels drop, releasing gasses (likely methane) from decomposed organic material. These ephemeral geological features not only provide insights into sediment dynamics but also highlight the complex interactions between geological processes, organic matter and carbon release.

Equally compelling is the rapid ecosystem recovery in areas previously submerged. "When these areas are exposed," Bowen explains, "we see native species returning surprisingly quickly. It challenges our assumptions about landscape resilience."

Assembling and working with instrumentation the group personified as "Esther" Credit: Elliot Ross

The Sediment Challenge

The researchers are keenly aware of the broader implications of their work. With an estimated eight percent of Lake Powell already filled with sediment, the reservoir's utility is finite. Current projections suggest the reservoir could be completely filled with sediment in 70-250 years, a nanosecond in geologic time. "Our primary message is simple," Johnson states. "Sediment is an integral part of water systems. You can't separate water management from sediment dynamics."

The research extends beyond local concerns. Bowen points out the global significance of their work: "Worldwide, reservoirs are disrupting sedimentary processes. We're both trapping sediment and increasing sedimentation rates through land development. This is a quintessential Anthropocene challenge."

 Looking forward, the researchers envision innovative approaches to data collection. Johnson dreams of a community science project where pilots, tourists and local flyers can contribute aerial photographs, providing additional perspectives on the rapidly changing landscape.

Capturing Change in Real-Time

Publications are typically the final resting place for research, but Johnson and Bowen’s priority is first capturing a moment of extraordinary geological transformation. "We're witnessing amazing landscape changes over short time scales," Bowen reflects. "Our role is to document, understand and help inform future management. It is both daunting and exciting to be collecting sedimentologic data with direct implications for important and pressing water management decisions." 

In the dynamic terrain of the American Southwest, these geologists are not just observing change — they're helping humanity understand its own impact on the natural world. And sedimentation is telling that story.

Researchers dwarfed by the massive escarpments of the canyon. Credit: Elliot Ross